The present invention relates to a process for the production of copper foil laminated plates. More particularly, the invention relates to a process for producing copper foil laminated plates using rolled copper foils made of oxygen-free copper with an oxygen content of not more than 50 ppm. These copper foil laminated plates are indispensable to electronic devices for the purpose of wiring.
A copper foil laminated plate for use in wiring of electronic devices basically is composed of an insulating hard or soft plastic substrate and a copper foil of a desired thickness bonded firmly to one or both sides of the plastic substrate by the use of a suitable adhesive.
In the production of conventional copper foil laminated plates, a so-called electrolytic copper foil produced by electrolytic deposition of a copper ion-containing solution has commonly been used as the copper foil. In general, however, adhesion between copper and plastics is inherently poor. Thus, in the case of electrolytic copper foils, a special surface treatment has been applied to the surface thereof to provide a very coarse surface structure. That is, the surface of electrolytic copper foil having fine irregulaties resulting from growth of copper crystals in the process of electrolytic deposition is further subjected to anodic oxidation to form a copper suboxide layer, in some cases a copper oxide layer, with a thickness of about several microns. The coarse surface structure increases the adhesion strength between the electrolytic copper foil and the adhesive. This results in an increase in the adhesion strength of the copper foil laminated plate as a whole.
Two problems have been encountered in producing copper foils for use in the conventional copper foillaminated plates: one is the difficulty of disposal of waste liquids from electrolytic deposition and anodic oxidation, and the other is that production costs are very high because the efficiency of electrochemical operations is poor.
As a result of extensive studies on high frequency transmission characteristics such as the tone quality of audio devices and resonance characteristics of TV video circuits, it has been found that copper suboxide or copper oxide formed on the surface of the copper foil for the purpose of increasing the adhesion strength exerts seriously large adverse influences on the high frequency response of such foil.
Moreover, when a circuit pattern is formed in the copper foil laminated plate by etching, copper suboxide or copper oxide particles remain in the insulating substrate embedded therein, even after the formation of the circuit. Thus the circuit is not suitable for practical use unless a strong etchant is applied to remove the copper suboxide or copper oxide particles. Application of such a strong etchant, however, undesirably causes so-called side etching. It is therefore not possible to reduce the circuit conductor spacings below a certain level when the conventional electrolytic copper foil made coarse by oxidation is used.